Process and apparatus for defined comminution of polymers gels

ABSTRACT

An apparatus and process for defined comminution of polymer gels, wherein the apparatus includes a static cutting element in the form of a cutting screen. The cutting element is optionally supported, and has pretensioned wires, rods, fibers, wovens, stencils or profiles. Optionally, a dynamic cutting element is provided for shortening the gel strands or particles obtained by means of the static cutting unit. Also, a feed unit is provided for feeding the polymer gel to the static cutting element in a clamped-in, shape-stable state. The feeding of the gel is effected batchwise or continuously.

This is a continuation application of Ser. No. 10/270,583, filed Oct.16, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to apparatus for comminuting polymer gels toobtain a defined, uniform particle size using a cutting unit comprisinga static cutting element with or without a dynamic cutting element andshape-stable feeding of the polymer gel to the cutting unit, and aprocess for performing the comminution.

2. Description of Related Art

Water-containing polymer gels are obtained from water-soluble monomersin the course of the production of water-soluble or water-swellablepolymers and are used in a very wide variety of fields. They are usedfor example as flocculation aids, drainage and retention aids, asviscosity-increasing agents in aqueous media, for example in tertiaryoil production, as grinding or dispersing assistants, adhesives,wastewater treatment agents, as superabsorbents in the hygiene andsanitary sector or as soil improvers in agriculture, as sealing agentsin the building construction industry and also in the production ofelectricity- and light-conducting cables or in medicine, for example tolower the cholesterol level by binding bile acids or bile acid salts orin the treatment of dialysis and predialysis patients to bindphosphates.

The production of the polymers or polymer gels, for example acrylic andallylic polymers, such as acrylic acid, methacrylic acid,hydroxyethylmethacrylic acid and acrylamide homopolymers and theirderivatives or copolymers composed of a major fraction of acrylic acid,methacrylic acid, hydroxyethylmethacrylic acid and acrylamidederivatives and other copolymerizable or crosslinking monomers, ofpolymer gels based on native or chemically modified proteins (eg gelatinand derivatives thereof) or of polymer gels based on natural orchemically modified homo- and heteropolysaccharides such as for examplestarch and cellulose, agarose, carageenan, chitosan, xanthan, guar gum,alginate, pectinate, sucrose gels, and also of polymer gels based onpolyelectrolyte-sucrose gels, and also of polymer gels based onpolyelectrolyte complexes, such as copper alginate for example, ofpolymer gels based on hydrolyzed crosslinked maleic anhydride copolymers(eg crosslinked hydrolyzed, partly neutralized maleic anhydride-methylvinyl ether copolymers or maleic anhydride-styrene copolymers), of N- oramino- or ammonium-containing polymers having cationic groups andsuitable counterions, which can contain hydrophobic groups, whereappropriate, is generally effected by bulk polymerization, suspensionpolymerization, emulsion polymerization or solution polymerization, asdescribed for example in EP-A1-068 189, EP-A1-0 415 141, EP-A-0 374 709,WO 00/38664, WO 99/33452, WO 99/22721, WO 98/43653, U.S. Pat. No.5,496,545, EP-A1-0 366 986, etc.

The polymer gels in question can be produced in 2 different ways.

a) By polymerization and partial crosslinking in a single step.

b) By subsequent crosslinking of a synthetic or natural polymer or ofderivatives thereof.

The prior art polymerization reaction is followed by appropriatecrosslinking (gelling). This provides, as a function of the monomers andcrosslinkers used and/or of the polymerization parameters, polymer gelswhich are water-containing, soft and rubbery or which are brittle andextremely shear sensitive.

The processing of these polymer gels to form powders is effected in thesubsequent process or workup steps, such as for example coarsecomminution, fine comminution, polymer-analogous chemical reaction,washing, separation, drying and grinding etc. and hitherto representedan appreciable cost and inconvenience if the polymer properties achievedin the gel state, such as for example swelling properties and particlestructure, and associated processing properties, such as for examplechemical convertibility, sedimentation capability, filtration speed,drying speed and grindability, were to be preserved. Thus, as describedin WO 96/36464 for example, the requisite uniformity of the processingsequence was already impaired by the precomminution and comminution ofthe soft, rubbery or brittle gels, since rubbery gel blocks or gelstrands are for example torn apart by kneaders into nonuniformly sizedpieces, whereas the division of soft gels produces with increasingplasticity gel portions having ever larger dimensions and the kneadingtools are often blocked by gel portions which have become wrappedthereon. This gives rise to an uneven flow of material, which leads todifferent layer thicknesses for example in foraminous belt drying andhence to an insufficient or excessive drying of the polymer withimpairment of the subsequent grinding and classifying operation andwhich, on the other hand, for example by hornification or by the partialthermal degradation of the polymer, gives rise to a reduction inquality, for example in swellability, the generation of toxic gases etc,and hence to inferior performance on the part of the product. In lieu ofkneaders it is generally also customary to use extruders, for example ameat grinder, to comminute polymer gels, by forcing the gel by means ofa conically narrowing single-screw conveying system through a breakerplate. However, this system is absolutely unsuitable for pressure- andshear-sensitive polymer gels, since the gel—even in the case of built-inrotating cutting blades—is more sheared than cut apart, which gives riseto enormous problems in the washing and the subsequent separation of thegels.

The literature, for example DE 35 39 385, DE 35 06 534 or WO 96/36464,discloses further comminuting processes and apparatuses, which, however,either have a very costly and inconvenient construction and/or imply acomplicated, costly or inconvenient comminuting operation or which aresuitable for coarse division only and in no instance lead to a uniformparticle distribution.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel apparatusand a process for the defined comminution of a polymer gel, especiallyof water-containing polymer gels, into uniform, preferably small,particles which, compared with the prior art, have improved properties,such as better controlled chemical convertibility, washability,separability, filterability, drying properties, grindability, coupledwith a reduced loss of fines in the respective separating and processsteps.

We have found that this object is achieved, unexpectedly, by apparatuscomposed of two or three main elements, namely a static cutting element,optionally a dynamic cutting element and a feeder which feeds the gel tothe cutting elements in a clamped-in or shape-stable state.

The present invention accordingly provides apparatus for definedcomminution of polymer gels, constructed of:

-   a) a static cutting element in the form of screen-shapedly disposed,    optionally supported, pretensioned wires, rods, fibers, wovens,    stencils or profiles;-   b) optionally a dynamic cutting element for shortening the gel    strands or particles obtained by means of the static cutting unit,    in the form of one or more optionally supported, guided and    tensioned wires or wovens; and-   c) a feed unit to feed the polymer gel to the static cutting element    in a clamped-in, shape-stable state the feeding being effected    batchwise or continuously.

The apparatus of the present invention is composed of two or three mainelements.

The first main element is the static screen-shaped cutting unit which iscomposed of optionally supported, pretensioned wires, rods, fibers,wovens, stencils or profiles.

Suitable wires, rods, fibers, wovens, stencils or profiles can becomposed not only of inorganic material, for example of optionallycoated, surface-finished metal, for example of alloyed or nonalloyedsteels, including stainless steels, iron, aluminum, copper, tantalum, orof glass, carbon, ceramic, boron, such as glass fiber, carbon fibers,ceramic fibers and boron fibers, etc, but also of polymeric organicmaterial, whether of wholly synthetic, partly synthetic or naturalorigin, such as for example of polyethylene (eg UHMW PE), polypropylene,polyesters, polyamides, aramid, polyetheretherketones (PEEKs),polysulfones, polytetrafluoroethylene, cellulose, etc.

Preference is given to using metal wires, rods, wovens or profiles orhigh strength polymeric fibers. Particular preference is given to wires,rods, wovens, stencils or profiles composed of stainless steel, springsteel or fibers of polyethylene (eg: Dyneema® UHME PE) and aramid (eg:Kevlar).

The shape or cross section of the wires and rods can be rectangular,square, triangular, hexagonal or round. The wires and rods usedpreferably have a square, triangular or round cross section and morepreferably a round cross section. A combination of the geometries isalso possible (square with triangular or round with triangular). But thewires and rods can also be flattened or beveled (sharpened) on one orboth sides. The diameter or thickness of the wires and rods is between0.05 and 10 mm, preferably between 0.08 and 6 mm and more preferablybetween 0.1 and 2.5 mm.

In the static cutting element, the wires, rods or fibers are disposed toform a screen in which the interspaces or mesh size correlate with thedesired shapes and dimensions, especially with the cross section of thecomminuted gel particles. The screen's interspaces can be triangular,square, rhombohedral, trapezoidal or rectangular, but preference isgiven to square interspaces. According to the invention, the interspaceshave a side length of 0.1 to 200 mm, preferably of 0.2 to 100 mm andmore preferably of 0.4 to 10 mm, whereby gel particles having a diametercorresponding to the dimensions chosen from the screen's interspaces areobtained.

When wires or fibers are used for the screen, it is advantageous forthem to be appropriately pretensioned (up to the yield point in the caseof metal wires) in order to create a defined uniform cutting geometry.The wires, rods and fibers of the screen may not be joined together ormay be joined together by weaving, looping, adhering, sintering, laserwelding, etc.

Instead of wires, rods or fibers, the static cutting element can also becomposed of a woven fabric or a stencil or profile. Suitable stencils orprofiles are preferably composed of metal and can be formed by diecutting, etching, laser machining, etc.

The stencil's interspaces can be disposed not only squarely,triangularly, rhombohedrally and trapezoidally, but also roundedly andpreferably hexagonally comb-shapedly, which yields advantages withregard to particle uniformity.

The dimensions of the interspaces are chosen as with the use of wires,rods or fibers.

The static cutting element is preferably formed of wires, woven mesh orrods and more preferably of wires and woven mesh.

The static cutting element can in principle be disposed bothhorizontally and vertically.

The static cutting element can optionally be equipped with a support.This is especially advantageous when using wires, fibers or wovens, toobtain better stability. The support can be realized in the form of amutually stiffening grid or a coarse wire cloth or in the form of ascreen which can also be configured as a screen fabric. It is preferableto use a grid to support the static cutting element.

The support is preferably rounded off on the side facing the staticcutting element in order that there may be no broken wire due tonotching between static cutting element and supporting grid.

The dimensions of this support are dependent on the size of the staticcutting element. The thickness of this support is dependent on thecutting forces to be applied to the gel to be cut (gel hardness) and onthe diameter of the screen or fabric to be supported. For example, thesupporting grid can be 80 mm for a diameter of 800 mm. The supportinggrid is likewise preferably of metal and more preferably of stainlesssteel and can where appropriate be welded into a ring for strengthreasons. In a preferred embodiment, the stays are half cut and pushedinto one another and are more preferably joined together by welding forstiffness reasons.

The support is directly mounted downstream of the static cuttingelement, so that adequate stabilization of the same is ensured duringthe comminution of the gels while at the same time the shape stabilityof the polymer gel is preserved. In the presence of a grid support, theshape-stable gel feed provides a clean cut similar in quality to thatobtained in the case of direct cutting immediately below or alongsidethe static cutting element. This applies particularly to comparativelysmall cut cross sections, where no supporting grid is needed on accountof the low deflection.

The supported or unsupported static cutting element is followed by asecond main element, a dynamic cutting element which serves to shortenthe gel strands or particles obtained by means of the static cuttingelement. However, if the gel strands are not cut any further, thedynamic cutting element is not needed.

According to the invention, the dynamic cutting element is composed ofone or more guided and tensioned wires or fibers or of wovens which, toimprove the uniformity of the particle length especially in the case oflarge diameters, can also be supported or guided. The support preventsany deflection on the part of the transverse cutting wires, which has aparticularly advantageous effect on the uniformity of the particlelength. The support in the most simple case can be composed of arelatively coarsely woven fabric, for example stainless steel orplastic, which is tensioned in a mobile frame. But the support for thetransverse cutting wires can also take the form of a plurality ofsupporting struts which are distributed over the clamped length andwhich have likewise been clamped into an appropriate mobile frame. Thesupporting struts preferably possess drilled holes into which have beeninserted drilled-through plastic bushes through which the tensionedtransverse cutting wires are passed. The plastic bushes provide asomewhat broader platform for the wire or fiber support and therebybring about a lower wire or fiber wear to distinctly improve the uselife of the dynamic cutting element.

According to the invention, the dynamic cutting element can be atensioned monowire which is disposed as a rotating, segmentally rotatingor traversing wire hoop.

A further embodiment of the dynamic cutting element is composed oftensioned wires which are disposed in a rotating spoked wheel having ahub. The number of wires depends on the speed of rotation of the cuttingwheel compared with the forward feed speed.

In another embodiment, the tensioned wires can also be disposed in agrate frame which moves back and forth in operation. It is of advantagehere for the wires to be equipped with additional stays for the purposeof guidance and support.

A fourth embodiment is a coarsely tensioned screen cloth which is movedback and forth in a grate frame. The wires, fibers and wovens used forthe dynamic cutting element can be composed not only again of inorganicmaterial, for example of optionally coated, surface-finished metal, forexample of alloyed and nonalloyed steels, including stainless steels,iron, aluminum, copper, tantalum, or of glass, carbon, ceramic, boron,such as glass fiber, carbon fibers, ceramic fibers and boron fibers,etc. but also of polymeric organic material, whether of whollysynthetic, partly synthetic or natural origin, for example ofpolyethylene (eg UHMW PE), polypropylene, polyesters, polyamides,aramid, polyetheretherketones (PEEKs), polysulfones,polytetrafluoroethylene, cellulose, etc. Preference is given to usingmetal wires or wovens or high strength polymeric fibers. Particularpreference is given to wires or wovens composed of stainless steel,spring steel or fibers of polyethylene (eg: Dyneema®; UHMW PE) andaramid (eg: Kevlar).

In the apparatus according to the invention, the dynamic cutting elementis always disposed at right angles to the press-out direction of thestatic cutter, although two further points are preferably observed foroptimum cutting quality.

Thus, the distance between the dynamic cutting element and the staticcutting element is preferably very small. The distance in the preferredembodiments is therefore preferably not more than 10 mm and morepreferably not more than 2 mm. Larger distances can likewise be chosen,but are disadvantageous if optimum cutting quality is to be obtained. Analternative, which allows larger distances between the dynamic andstatic cutting elements while at the same time ensuring optimum cuttingquality, is that the particles cut with the static cutting element areforwarded in a shape-stable state in a clamped-in, self-stiffening gridto the dynamic cutting element, which is placed directly at thedownstream end of the grid.

A second important point concerns the cutting speed of the dynamiccutting element. The faster the cutting speed of the dynamic cuttingelement, the less the soft and flexible particles are able to bend awayfrom or evade the cut. The higher consequently the cutting speed of thedynamic cutting element compared with the forward feed speed of thepolymer gel, the better the quality of cut.

The ratio of the cutting speed of the dynamic cutting element to theforward feed speed of the gel strands has an influence on the shape anduniformity of the cut particles. This is especially the case in thegrate embodiment (traversing movement) of the dynamic cutting unit.

The cutting speed of the dynamic cutting unit in the apparatus accordingto the invention is preferably not less than the forward feed speed ofthe polymer gel or gel strands. It is preferable to have a ratio of atleast 2:1 and particularly of at least 10:1 for cutting speed to forwardfeed speed. Slower cutting speeds can also be chosen, but they do nothave an advantageous effect on cutting quality.

The third main element is the feed unit to feed the polymer gel to becut to the static cutting element in a shape-stable, clamped-in state.This shape-stable feed can be effected batchwise or continuously.

In the batchwise version, the polymer gel is fed to the cutting elementsvia a closeable chest by means of a horizontal plunger press-out device.For this, the gel is first coarsely precut into blocks which are thencharged into the chest. A lever is used to shift, i.e. enlarge, thefront part of the chest in the course of filling, to facilitate thechest-filling operation. The chest is sealed at the top by a bladelikeslider and the front part of the chest is pushed forward to such anextent that there is a slight sideways press which does not impair theforward movement of the rectangular press plunger (1), yet a sealed-offspace is formed nonetheless, whereby the gel polymer blocks are fed in aclamped-in, shape-stable state to the cutting elements.

In a further preferred batchwise version, the polymer gel is pressed outof a tubular container in which the production of the polymer gel orcrosslinking of the polymers is effected.

The container has a removable lid and a removable base with appropriateseals. As the container is fed to the cutting unit, the lid is removedfirst. The base is preferably removed by passing the container over acentering flange. In the process, the base of the container ispreferably forced over a shear-off edge, for example of plastic,preferably of Teflon, or over a plastic-coated or -clad, preferablyTeflon-coated or -clad, shear-off edge, whereby the container base isleft lying upstream of the shear-off edge and the container is at thesame time pushed onto the centering flange, so that the polymerstructure of the gel is not destroyed. In order that the lower containerseal, preferably a dovetailed seal, may not be damaged, the container isslightly raised during the shearing off of the container base,preferably by means of lateral rollers attached to the container andappropriate guide rails, and lowered back onto the centering flange whenarriving at the latter. The pressing-out of the polymer gel can bestarted when the container is situated on the centering flange, which isdisposed centrically above the static cutting element, and a fixation ofthe container has taken place, for example by means of clamping tongs,which are operated electromagnetically, hydraulically or pneumaticallyfor example.

In this embodiment of the invention, the pressing-out is effected bymeans of a press plunger which is centeredly introduced into thecontainer at the desired forward feed speed. To ensure centeredintroduction into the container, the press plunger is preferably mountedin a ball socket, so that it is moveable in all directions and theplunger's own weight causes it to fall into the perpendicular position.The container further preferably has a centrical bevel which likewisefacilitates the centrical introduction of the press plunger.

However, the polymer gel can also be fed continuously. This isparticularly the case when the production of the polymer gel is effectedin a continuous manner in a tubular reactor, for example similarly toEP-0 374 709. The contained process in the case of the continuous feedoffers an immense advantage with regard to product and occupationalhygiene.

Preferred combinations of the apparatus according to the invention arecomposed of:

-   -   a) a horizontally disposed press plunger (pressing means), a        chest, a static cutting screen and a cutting wheel; or of    -   b) a standing or hanging press plunger, a container in which the        production of the polymer gel is effected, a static cutting        screen and the grate embodiment of the dynamic cutting element;        or    -   c) for the continuous embodiment, of a continuous tubular        reactor with static cutting screen, optionally with supporting        grid and a cutting wheel; or    -   d) for the continuous embodiment, of a continuous tubular        reactor with a static cutting screen, optionally with supporting        grid and the grate embodiment of the dynamic cutting element.

The abovementioned object is further achieved according to the inventionby a process for defined comminution of polymer gels, preferably ofwater-containing polymer gels, which comprises using the apparatusaccording to the invention to cut the polymer gel directly afterpolymerization or crosslinking of the polymer into polymer gel particlesof uniform size. To this end, the gel is fed by the feeding unit in ashape-stable, clamped-in state to the static cutting element and ispressed therethrough at a certain forward feed speed, whereupon theresulting gel strands are, where appropriate, cut by the dynamic cuttingelement, as a function of the chosen cutting speed, into uniformparticles having the desired dimensions (lengths).

The apparatus and process according to the invention provide definedcomminution of the polymer gels into uniform particles which, comparedto the prior art, have improved properties, such as better washability,controlled chemical convertibility, separability, filterability, dryingproperties, grindability, coupled with a reduced loss of fines in therespective separating and processing steps.

The particles obtained according to the invention are prismaticparticles of preferably square geometry or are cylindrical particles.The length of the prisms or cylinders can vary from 0.1 mm up to thenatural breaking length. Preferably, however, the cut length is between0.2 and 100 mm and more preferably between 0.4 and 10 mm. The diameterof the particles is dictated as described above by the dimensions of thescreen or screen interspaces of the static cutting element and is 0.1 to200 mm, preferably 0.2 to 100 mm and more preferably 0.4 to 10 mm. Morepreferably, the cut particles have a cubic shape or a ratio of 1:1 forprism or cylinder height to prism or cylinder diameter.

The apparatus and process according to the invention are useful forpolymer gels, preferably for water-containing polymer gels, for examplefor acrylic and allylic polymers, such as acrylic acid, methacrylicacid, hydroxyethylmethacrylic acid and acrylamide homopolymers and theirderivatives or copolymers composed of a major fraction of acrylic acid,methacrylic acid, hydroxyethylmethacrylic acid and acrylamidederivatives and other copolymerizable or crosslinking monomers, forpolymer gels based on native or chemically modified proteins (eg gelatinand derivatives thereof) or for polymer gels based on natural orchemically modified homo- and heteropolysaccharides such as for examplestarch and cellulose, agarose, carageenan, chitosan, xanthan, guar gum,alginate, pectinate, sucrose gels, and also for polymer gels based onpolyelectrolyte complexes, such as copper alginate for example, forpolymer gels based on hydrolyzed crosslinked maleic anhydride copolymers(eg crosslinked hydrolyzed, partly neutralized maleic anhydride-methylvinyl ether copolymers or maleic anhydride-styrene copolymers), and forN- or amino- or ammonium-containing polymers having cationic groups andsuitable counterions, which can contain hydrophobic groups.

Suitable polymers and polymer gels are known for example from EP-A1-068189, EP-A1-0 415 141, EP-A-0 374 709, WO 00/38664, WO 99/33452, WO99/22721, WO 98/43653, U.S. Pat. No. 5,496,545, EP-A1-0 366 986, etc.

The apparatus and process according to the invention are each preferablyused for cutting crosslinked, aqueous polymer gels, more preferably N-or amino- or ammonium-containing polymers with cationic groups andsuitable counterions, which may optionally contain hydrophobic groups.

Embodiments of the apparatus according to the invention are depicted inFIGS. 1 to 3 and will now be more particularly described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment according to theinvention,

FIG. 2 is a perspective view of a further embodiment according to theinvention,

FIG. 3 is a perspective view of a detail of the cutting elements of FIG.2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an apparatus composed of a horizontally disposed pressplunger (pressing means) (1), a chest with sideways prepress and lid(2), a static cutting element with cutting screen (3) and a cuttingwheel with cutting wires (4) as a dynamic cutting element.

FIG. 2 shows an apparatus composed of a hanging press plunger (5), acontainer in which the production of the polymer gel is effected(gelling drum) (6), a static cutting element with cutting screen andsupporting grid (7) and the dynamic cutting element with cutting gratewith cutting wire guidance (8).

FIG. 3 shows the cutting elements of FIG. 2, showing the cutting screen(7 a) and the supporting grid (7 b) of the static cutting element andalso the cutting wires (8 a) with the cutting wire guidance (8 b) of thedynamic cutting element.

EXAMPLE 1 a) Description of Polymer Gel

This patent example utilized a crosslinked, aqueous polyallylamine. Tothis end, 277 kg of a 19% aqueous polyallylamine solution (molecularweight: 20 000) were thoroughly homogenized with 3.17 kg ofepichlorohydrin at a pH of 10 and at a reaction temperature of 20° C.over a period of 30 minutes. This mixture was then allowed to cure in agelling vessel at room temperature for at least 30 hours. The result wasan extremely shear-sensitive polymer which could not be comminuted withknives without a significant production of fines.

b) Cutting Operation Using a Cutting Apparatus as Per FIG. 1:

To this end, a Mustang 100-CE machine from TREIF was adapted with aninventive static cutting element suitable for these purposes and with adynamic cutting element. A closeable cutting chamber was filled with theabove-described crosslinked polyallylamine (polymer gel). It wasnecessary for this that the polymer gel had already been prepared inthis shape or had been appropriately precomminuted into suitable blocks.The chest was filled by hand. The polymer gel-filled chest wassubsequently sealed by means of a lever mechanism and a moveable blockof plastic which has the function of a lateral seal. A moveable metalslide formed into a blade closed the fill inlet off from above. Theclosing pressure of the chest was adjustable and could be adapted to thepressure sensitivity of the polymer gel. One side of the chest wasclosed off by the withdrawn press plunger, which was in the startingposition. The static cutting element was on the side opposite the pressplunger. The press plunger forced the polymer gel contained in the chestthrough the static cutting element (cutting screen), cutting the polymerparticles into endless strands. However, the dynamic cutting elementimmediately adjoining the static cutting element did not cut any endlessstrands, but cut very uniform polymer particles. The static cuttingelement was composed of tensioned monowires which were disposed in acrossed arrangement. The monowires were tensioned using a suitableguidance and by means of a suitable tensioning apparatus. The dynamiccutting element used was a spoked wheel having 24 tensioned wires. Thespeed of rotation of the spoked wheel was adjustable, making it possibleto adjust the particle length as a function of the forward feed speed.

c) Materials and Cutting Parameters:

Piston composed of Teflon; other product-contacted parts composed ofstainless steel

Piston dimensions: 96×96 mm

Chest dimensions: 96×96×550 mm

Length of lateral plastic block: 590 mm

Forward feed speed: 30 mm/s

Static Cutting Element:

Number of tensioned longitudinal wires: 48 off

Number of tensioned transverse wires: 48 off

Wire thickness: 0.5 mm

Wire spacing: 1.5 mm (mesh size)

Arrangement of wires: square

Dimensions of clear area of cutting screen:

96×96 mm

Wire material: 1.4571 (V-4A)

Dynamic Cutting Element: Spoked Wheel

Spoked wheel outside diameter: 465 mm

Stay width of outer wheel: 11.5 mm

Clear cutting wire length: 183 mm

Hub outside diameter: 77 mm

Wire thickness: 0.5 mm (1.4571)

The distance between the static and dynamic cutting elements was 1 mm.Evaluation of cut outcome: cubic particle sizeSize: about 1.5 mm; virtually no fines

The comminuted polymer gel thus produced was admixed with 2 times theweight of methanol and subsequently stirred for 15 minutes and rated forsedimentation capability and filterability. The results are summarizedin table 1.

EXAMPLE 2

The crosslinked polyallylamine described in example 1 was used. Afterstirring at room temperature for about 30 minutes, it was filled whilestill liquid into a tubular container with detachable base and lid.

Following a curing time of 30 hours, the gel was comminuted in thehereinbelow indicated apparatus as per FIG. 2.

Material of cylindrical container, of base and of lid: (1.4571)stainless steel. The inner surface of the container had beenelectropolished and had an average roughness depth of Ra<0.5 μm.

Immediately before the partly crosslinked aqueous polymer gel waspressed out, the cylindrical vessel, with base and lid removed, wasplaced via a centering flange above the cutting tool.

The press plunger was composed of a 1.4571 stainless steel plate coatedwith Teflon.

Container Dimension:

Internal diameter: 800 mmContainer length: 700 mmAmount of polymer gel: 280 kg

Dimensions of Static Cutting Element: Diameter: 800 mm

Mesh size: 1.4×1.4 mm; wire thickness 0.45 mm (from Haver & Boecker).Fabric material: 1.4571 stainless steel

This woven mesh was pulled over a tensioning ring and adhered theretousing a 2-component adhesive. The woven mesh was further supported witha supporting grid.

Dimensions of Supporting Grid:

100×100 mm in square: grid height: 80 mmDynamic cutting element: grate with 9 tensioned longitudinal wiressupported 3 times in the center.Grate traverse length: 100 mmWire thickness: 0.5 mmMaterial: 1.4401 spring steel wire

Cutting Parameters:

Forward feed speed of press plunger: 30 mm/minDistance between supporting grid and cutting grate: 1 mmCutting speed: 100 mm/sEvaluation of cut outcome: cubic particle sizeParticle size 1.4 mm; virtually no fines

The comminuted polymer gel thus produced was admixed with 2 times theweight of methanol and subsequently stirred for 15 minutes and rated forsedimentation capability and filterability. The results are summarizedin table 1.

EXAMPLE 3

The material used was a polyallylamine crosslinked similarly to example1, except that 1.57 times the crosslinker fraction was used. Thiscrosslinked polymer gel was comminuted similarly to example 1.

The comminuted polymer gel thus produced was admixed with 2 times theweight of methanol and subsequently stirred for 15 minutes and rated forsedimentation speed and filtration speed. The results are summarized intable 1.

EXAMPLE 4

The same polymer as in example 1 was used and the cutting apparatus asper FIG. 2 was used.

Tubular container with detachable base and lid.Press plunger: 1.4571 material provided with a 20 mm thick nylon-6,6plate.

Container Dimensions:

Internal diameter: 800 mmSurface finish: electropolished, roughness depth<0.5 μmContainer length: 700 mmAmount of polymer gel: 340 kgDimensions of static cutting screen: diameter: 800 mmMesh size: 1.4×1.4 mm; wire thickness 0.28 mm (from Haver & Boecker).Fabric material: 1.4401Supporting grid: grid 100×100 mm; grid height: 80 mmDynamic cutting element: cutting grate in moveable frame having 9tensioned longitudinal wires supported 3 times in the middle.Grate traverse length: 100 mmWire thickness: 0.28 mmMaterial of wires: 1.4401

Cutting Parameters:

Forward feed speed of press plunger: 60 mm/minParticle length: cubic 1.4 mmCutting speed of dynamic cutting grate: =100 mm/s

The comminuted polymer gel thus produced was admixed with 2 times theweight of methanol and subsequently stirred for 15 minutes and rated forsedimentation capability and filterability. The results are summarizedin table 1.

EXAMPLE 5

Same as example 2, except cutting length 0.5 mm length.

EXAMPLE 6

Same execution as example 2, except cutting length 5 mm.

EXAMPLE 7

Same execution as example 2, except a tensioned polymeric fabric wasused as static cutting element.

Material: polypropylene (manufacturer: SEFAR/CH).Style: Sefar Propyltex 05-3360/60; woven fabric with square meshesDimensions: w=30 mm; d=1.0 mm, (w=mesh size; d=fiber thickness)Cut outcome: cubic, 3 mm; virtually no fines.

EXAMPLE 8

Same execution as example 2, but a UHMW PE fiber (Dyneema, from DSM/NL)was used for the cutting grate.

Cut outcome: cubic, 1.4 mm; virtually no fines.

EXAMPLE 9

Same as example 1, except that the polymer gel used was a 5% by weightcarrageenan solution which was boiled up for 1 minute and subsequentlycooled down to room temperature.

Cut outcome: cubic, 1.5 mm; virtually no fines.

EXAMPLE 10

Same as example 1, except that the polymer gel used was an acrylamidecopolymer. This polymer gel was produced similarly to EP 415 141 B1.

A 50 liter reactor was charged at 20° C. with 15 kg of deionized waterfollowed by 12 kg of 50% (w/w) of aqueous acrylamide solution and 4.3 kgof 50% (w/w) of aqueous sodium acrylamidomethylpropanesulfonate solutionand then by 0.002 kg of methylenebis-acrylamide. After intimate mixing,hydrochloric acid was used to set a pH of 5. After purging with nitrogenfor 30 minutes, the polymerization was initiated. The initiator used was0.5 g of Na₂S₂O₅ and 1 g of (NH₄)₂S₂O₈, which were added in 1 kg ofwater. The polymerization was carried out adiabatically and ended in thecourse of 2 hours.

This gel was comminuted with the apparatus as described in example 1.

Evaluation of Cut Outcome:

Particle length: 1.5×1.5×2 mm; virtually no fines.

EXAMPLE 11 Continuous Polymerization

The polymerization was carried out similarly to patent example 1described in EP 0 374 709 A2. The monomer mixture, initiator combinationand release liquid described in example 1 of EP 0 374 709 A2 was used.

A vertical Teflon-coated metal tube 200 mm in diameter and 4 m in lengthwas used. At the beginning, the tubular reactor sealed with a Teflonplate was half filled with polymer solution and this polymer solutionwas polymerized under adiabatic conditions for 2 hours.

The metal plate was then removed and the cutting tool attached. Themonomer solution and initiator solution were separately and continuouslyhomogenized by means of metering pumps tangentially in a dynamic mixingchamber having a high-speed stirrer and then this homogeneouspolymerization solution was continuously fed by a high-pressure pistonpump to the tubular reactor. The adiabatic regime caused the temperatureto rise to about 80° C. The feed was 62 kg/hour.

The static cutting tool was a woven square mesh having a mesh size of1.4 mm and a wire thickness of 0.45 mm which was pretensioned betweentwo flanges and adhered with a 2-component system. A cross (as thesimplest form of a grid) was welded into the tube underneath the staticcutting fabric to support the static cutting fabric. The dimension ofthe supporting cross: sheet metal thickness 1.5 mm, round at the top,inserted into each other and welded together; height: 50 mm; similarlywelded to the outer wall of the stainless steel tube.

Distance between static and dynamic cutting elements was 1 mm.

The dynamic cutter was embodied as a rotating cutting hoop which wasoperated at a speed of rotation of 16 rpm.

The cut polymer gel obtained was virtually free of fines and thedimensions of the prismatic particles were 1.4×1.4×2 mm.

EXAMPLE 12 Comparative Example

The polymer gel produced under example 1 was comminuted in a LASKA W-130meat grinder.

The diameter of breaker plate was 130 mm.

The polymer gel was forced by the meat grinder through a breaker platehaving holes 3.5 mm in size. Number of blades: 4 off.

EXAMPLE 13 Determination of Sedimentation Capability and filterability

The comminuted polymer gels thus produced were admixed with 2 times theweight of methanol and subsequently stirred for 15 minutes and rated forsedimentation capability and filterability. The results are summarizedin Tab. 1 as well as the particle morphology and particle dimensions.

Comparison of comminuted gel polymers:

Sedimentation Wash- and Particle capability filterability Ex. # Finesdimensions in MeOH in MeOH 1 virtually cubic, good good no fines 1.5 ×1.5 × 1.5 mm 2 virtually cubic, very good very good no fines 1.4 × 1.4 ×1.4 mm 3 virtually cubic, good very good no fines 1.5 × 1.5 × 1.5 mm 4virtually cubic, very good very good no fines 1.4 × 1.4 × 1.4 mm 5virtually Prismatic, very good good no fines 1.4 × 1.4 × 0.5 mm 6virtually prismatic, very good very good no fines 1.4 × 1.4 × 5 mm 7virtually cubic, very good very good no fines 3 × 3 × 3 mm 8 virtuallycubic, very good very good no fines 1.4 × 1.4 × 1.4 mm 9 virtuallycubic, good good no fines 1.5 × 1.5 × 1.5 mm 10  virtually prismatic,good good no fines 1.5 × 1.5 × 2 11  virtually prismatic, good good nofines 1.4 × 1.4 × 2 Comparative undefined very broad very slow virtuallyunfilterable. example 12 particle size, particle sheared distributionfrom product 20 μm to 500 μm

1. An apparatus for comminution of polymer gel, said apparatuscomprising: a static cutting unit including a cutting screen forobtaining gel strands, wherein the cutting screen is formed ofpretensioned members, and the static cutting unit includes a stiffeninggrid for supporting the cutting screen; a dynamic cutting element,positioned downstream of the static cutting unit, for cutting the gelstrands formed by the static cutting unit into particles of uniform sizeand shape; and a feed unit for feeding the polymer gel to the staticcutting unit in a shape-stable state, wherein the feed unit is operableto feed the polymer gel batchwise or continuously.
 2. The apparatus asclaimed in claim 1, wherein the feeding unit comprises a tubularcontainer and a plunger positioned in the container, and the dynamiccutting element comprises a plurality of wires supported by a guidestructure that is movable in a direction that is transverse relative tothe feed direction of the container.
 3. A process of comminuting polymergels with the apparatus of claim 1, the process comprising: polymerizingor crosslinking a polymer to form a polymer gel; and feeding the polymergel to the static cutting screen and forcing the polymer gel through thestatic cutting screen to cut the polymer gel into a plurality ofstrands.
 4. The process as claimed in claim 3, further comprisingcutting the strands into uniform polymer particles with the dynamiccutting element positioned adjacent the static cutting element.
 5. Theprocess as claimed in claim 3, wherein the polymer gel is fed by thefeeding unit in a shape-stable state and at a predetermined speed to thecutting screen.
 6. The process as claimed in claim 3, further comprisingprecutting the polymer gel into blocks and placing the blocks in thefeeding unit which includes a closable chest and a horizontal plunger,wherein the blocks of polymer gel are fed in a shape-stable state and ata predetermined speed to the cutting screen.
 7. The process as claimedin claim 3, further comprising cutting the strands into uniform polymerparticles with the dynamic cutting element, wherein the dynamic cuttingelement comprises a rotatable spoked wheel which is rotated at apredetermined cutting speed, and the ratio of the cutting speed to thepolymer gel feed speed is at least 2:1.
 8. The process as claimed inclaim 7, wherein the uniform particles cut by the dynamic cuttingelement are uniform prismatic particles or cylindrical particles havinga prism or cylinder length of 0.1 mm to 100 mm and a diameter of 0.1 to200 mm, and wherein the shape of the particles is dependent upon theshape of the openings formed in the static cutting screen.